CVE-2025-21891 [Medium] | Security Vulnerability in Linux Kernel

In the Linux kernel, the following vulnerability has been resolved: ipvlan: ensure network headers are in skb linear part syzbot found that ipvlan_process_v6_outbound() was assuming the IPv6 network header isis present in skb->head [1] Add the needed pskb_network_may_pull() calls for both IPv4 and IPv6 handlers. [1] BUG: KMSAN: uninit-value in __ipv6_addr_type+0xa2/0x490 net/ipv6/addrconf_core.c:47 __ipv6_addr_type+0xa2/0x490 net/ipv6/addrconf_core.c:47 ipv6_addr_type include/net/ipv6.h:555 [inline] ip6_route_output_flags_noref net/ipv6/route.c:2616 [inline] ip6_route_output_flags+0x51/0x720 net/ipv6/route.c:2651 ip6_route_output include/net/ip6_route.h:93 [inline] ipvlan_route_v6_outbound+0x24e/0x520 drivers/net/ipvlan/ipvlan_core.c:476 ipvlan_process_v6_outbound drivers/net/ipvlan/ipvlan_core.c:491 [inline] ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:541 [inline] ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:605 [inline] ipvlan_queue_xmit+0xd72/0x1780 drivers/net/ipvlan/ipvlan_core.c:671 ipvlan_start_xmit+0x5b/0x210 drivers/net/ipvlan/ipvlan_main.c:223 __netdev_start_xmit include/linux/netdevice.h:5150 [inline] netdev_start_xmit include/linux/netdevice.h:5159 [inline] xmit_one net/core/dev.c:3735 [inline] dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3751 sch_direct_xmit+0x399/0xd40 net/sched/sch_generic.c:343 qdisc_restart net/sched/sch_generic.c:408 [inline] __qdisc_run+0x14da/0x35d0 net/sched/sch_generic.c:416 qdisc_run+0x141/0x4d0 include/net/pkt_sched.h:127 net_tx_action+0x78b/0x940 net/core/dev.c:5484 handle_softirqs+0x1a0/0x7c0 kernel/softirq.c:561 __do_softirq+0x14/0x1a kernel/softirq.c:595 do_softirq+0x9a/0x100 kernel/softirq.c:462 __local_bh_enable_ip+0x9f/0xb0 kernel/softirq.c:389 local_bh_enable include/linux/bottom_half.h:33 [inline] rcu_read_unlock_bh include/linux/rcupdate.h:919 [inline] __dev_queue_xmit+0x2758/0x57d0 net/core/dev.c:4611 dev_queue_xmit include/linux/netdevice.h:3311 [inline] packet_xmit+0x9c/0x6c0 net/packet/af_packet.c:276 packet_snd net/packet/af_packet.c:3132 [inline] packet_sendmsg+0x93e0/0xa7e0 net/packet/af_packet.c:3164 sock_sendmsg_nosec net/socket.c:718 [inline]

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-05	0.09%	0.02%	-0.07%
2	2026-01-21	0.02%	0.09%	+0.07%
3	2025-03-28	—	0.02%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-05

0.09%

0.02%

-0.07%

2026-01-21

0.02%

0.09%

+0.07%

2025-03-28

—

0.02%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
5.5	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	3.6	[email protected]
5.5	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	3.6	134c704f-9b21-4f2e-91b3-4a467353bcc0

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

5.5

3.1

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

3.6

[email protected]

5.5

3.1

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

3.6

134c704f-9b21-4f2e-91b3-4a467353bcc0

OS Trackers for CVE-2025-21891

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2025-21891 not yet assigned priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5, open 1.	https://security-tracker.debian.org/tracker/CVE-2025-21891
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2025-21891
`suse`	medium	—	https://www.suse.com/security/cve/CVE-2025-21891/
`ubuntu`	medium	CVE-2025-21891 medium priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1551 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1145, ignored 153, released 138, needed 74, not-affected 41.	https://ubuntu.com/security/CVE-2025-21891

Affected software / configurations for CVE-2025-21891

Vendor	Product	Version	Raw CPE
linux	linux_kernel	>= 3.19, < 6.1.130	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.2, < 6.6.81	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.7, < 6.12.18	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.13, < 6.13.6	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc1::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc2::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc3::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc4::::::

References for CVE-2025-21891

URL	Tags
https://git.kernel.org/stable/c/27843ce6ba3d3122b65066550fe33fb8839f8aef	Patch
https://git.kernel.org/stable/c/4ec48f812804f370f622e0874e6dd8fcc58241cd	Patch
https://git.kernel.org/stable/c/5353fd89663c48f56bdff975c562cfe78b1a2e4c	Patch
https://git.kernel.org/stable/c/5b8dea8d1612dc7151d2457d7d2e6a69820309bf	Patch
https://git.kernel.org/stable/c/e2a4f76a2d8a44816ecd25bcbdb47b786d621974	Patch
https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html

URL

CVE-2025-21891 | ipvlan: ensure network headers are in skb linear part

Exploit prediction scoring system (EPSS) score for CVE-2025-21891

Common vulnerability scoring system (CVSS) metrics for CVE-2025-21891

Weakness enumeration for CVE-2025-21891

OS Trackers for CVE-2025-21891

Affected software / configurations for CVE-2025-21891

References for CVE-2025-21891